The invention relates to a servo-assisted rack-and-pinion steering system in which the rack cooperates with a pinion. The pinion is capable of limited movement transversely or, in particular, parallel to the longitudinal axis of the rack. The movements of the pinion, which occur through constraint when forces are transmitted between the pinion and the rack, actuate the servomotor or its control elements.
A corresponding servo steering system is known, for example, from German Patent document DE 42 03 335 A1. There, the pinion is fastened in a fixed bearing at its axial end which is to be connected to the steering wheel, while the other axial end of the pinion is mounted in a movable bearing. On the transmission of forces between the pinion and the rack, the pinion axis is accordingly constrained to make swivelling movements. These swivelling movements are transmitted via parts of the movable bearing to push rods of a servo valve arrangement, by which a hydraulic servomotor is controlled.
In a rack-and-pinion steering system of the type described above known from German Patent document DE 40 36 743 A1, the pinion is mounted axially and radially in a sleeve. The sleeve is provided in the region of the rack with a window enabling the pinion to engage in the rack. The sleeve is fastened for swivelling about an axis which is parallel to the pinion axis and is situated on that side of the plane of the rack toothing which is remote from the pinion axis. When forces are transmitted between the pinion and the rack, the sleeve then makes swivelling movements together with the pinion. This has the consequence that the pinion axis is displaced sideways in one direction or the other, relative to a normal position, parallel to the longitudinal axis of the rack. Through a lever-like radial extension arranged on the sleeve, this swivelling movement is transmitted to the valve slide of a servo valve arrangement in order to control a hydraulic servomotor.
In these known designs, it is not possible to preclude the undesired occurrence of pinion movements which act on the servomotor.
There is therefore needed a steering system design of the type described above which, kinematically, is markedly improved.
According to the present invention, this need is met in that the pinion is connected to a shaft part, connected to it, through a coupling permitting misalignment of axes, for example, according to the "Oldham" system.
The invention is based on the general principle of suppressing the ability of a steering system to transmit radial forces between the pinion and the steering shaft or the like, which is to be connected to it for driving purposes, so that substantially only torques can be transmitted.
A high degree of design freedom with respect to the installation and construction of the steering shaft, or of the parts to be connected to the pinion for the driving connection to the steering wheel, is thus achieved. In particular, these parts can have comparatively resilient mountings.
At the axial end remote from the coupling, the pinion is preferably mounted using a self-aligning bearing, so that the pinion axis can oscillate about the center of this bearing.
A part arranged axially between the coupling and the toothing part of the pinion can directly actuate a servo valve arrangement, for example, using push rods which are arranged to be slidable, against spring force, by means of the aforesaid part of the pinion.
If the servomotor works hydraulically, as is usually expedient, the return flow of the hydraulic medium to a reservoir or tank is made to pass through a casing part, embracing the coupling, of the rack-and-pinion steering system. This is done so that the coupling permitting axis misalignment between the pinion and the shaft part is continuously force-fed with lubricant and remains easy-running.
In this case, the return flow can pass through axial channels in the aforesaid push rods.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.